1. Field of the Invention
The present invention relates to wireless communication systems, and more particularly relates to a data communication method based on packet aggregation that can improve transmission efficiency and minimize power loss in a wireless communication system based on multiple carriers.
2. Description of the Related Art
Conventional communication systems use a hierarchical frame structure to efficiently transmit high layer data. Specifically, packet aggregation in a media access control (MAC) layer and a physical layer (PHY) is being studied and developed to maximize the efficiency of radio resources of communication systems which conform to wireless communication standards such as the Institute of Electrical & Electronic Engineers (IEEE) 802.11 and 802.16 standards.
Aggregation schemes include single receiver aggregation (SRA) for aggregating packets destined for a single station (STA) to transmit the aggregated packets in one physical layer (PHY) protocol data unit (PPDU), and multi-receiver aggregation (MRA) for aggregating packets destined for multiple STAs to transmit the aggregated packets in one PPDU.
MRA schemes are classified into an MRA scheme based on a single transmission rate for applying the same transmission rate to packets to be transmitted to different destinations using a single PPDU and an MRA scheme based on multiple transmission rates for applying a transmission rate suitable for packets according to each destination within the PPDU.
A packet aggregation scheme includes an MRA scheme based on a single transmission rate proposed by the task group N synchronization (TGnSync) and a high throughput (HT)-burst scheme proposed by the World Wide Spectrum Efficiency (WWiSE) group as two representative schemes proposed by the IEEE 802.11 TGn standard.
FIG. 1 illustrates the format of an MRA proposed by the TGnSync group. The MRA includes an MRA descriptor MAC protocol data unit (MRAD MPDU) 101 including receiver addresses (RAs), and a plurality of STA-by-STA MPDU groups 103, 105, and 107 each including an initiator aggregate control (IAC) MPDU 102 and data MPDUs 104 to be transmitted to the RAs. The MPDUs 104 are identified by MPDU delimiters (MDs) 109.
The MRAD MPDU 101 includes the RAs of MPDUs included in the MRA. Because a reception STA can determine, in advance (i.e., before reception), if a packet to be received is present in a PPDU, the a reduction in reception power can be achieved. However, this MRA scheme is based on the single transmission rate, and must use the lowest transmission rate because all reception STAs must be able to receive the MRA, despite that an optimal transmission rate is available according to the distance between reception STAs or channel characteristics. Therefore, the efficiency of transmission resources is reduced.
FIG. 2 illustrates the format of conventional high throughput HT-burst proposed by the WWiSE group. In FIG. 2, the HT-burst includes PPDUs or aggregation PPDUs (A-PPDUs) configured by frames on an STA-by-STA basis. In other words, a first PPDU 201 includes Frame #0 210 and Frame #1 211 whose destinations are STA #1), a second PPDU 202 includes Frame #2 212, a third PPDU 203 includes Frame #3 213 and a fourth PPDU 204 includes Frame #4 214 and Frame #5 215.
When successive frames are transmitted at the same power in the conventional HT-burst scheme, the next frame is transmitted on the basis of zero interframe space (ZIFS). When successive frames are transmitted at different power in the HT-burst scheme, the next frame is transmitted on the basis of reduced interframe space (RIFS). Here, the transmission power variation indicates the transmission rate variation. The conventional HT-burst scheme does not take into account reception power reduction and has only an STA-by-STA aggregation effect. As an A-PPDU transmission interval is reduced, a small benefit may be expected. However, a multi-STA aggregation effect is, for the most part, insignificant, in the conventional HT-burst scheme.